Modification of surface morphology of hydrogels due to subsurface femtosecond laser micromachining.

In this paper, we studied the effects of subsurface femtosecond laser micromachining on surface morphology in hydrogels. Depending on material properties and writing conditions, we found surface bumps when materials were hydrated, and trenches when they were dehydrated, which can be attributed to the localized change in water concentration. Such wavy surfaces by laser-induced refractive index change are not desirable in clinical contact lenses. Therefore, the minimization of surface bumps is necessary to ensure the user eye wearing comfort. In addition, we examined the optical effects of the surface features using interferometry and the surface morphology using profilometry. Finally, we proposed a simplified mechanical model based on localized swelling.

Implantable photonic neural probes with out-of-plane focusing grating emitters.

We have designed, fabricated, and characterized implantable silicon neural probes with nanophotonic grating emitters that focus the emitted light at a specified distance above the surface of the probe for spatially precise optogenetic targeting of neurons. Using the holographic principle, we designed gratings for wavelengths of 488 and 594 nm, targeting the excitation spectra of the optogenetic actuators Channelrhodopsin-2 and Chrimson, respectively. The measured optical emission pattern of these emitters in non-scattering medium and tissue matched well with simulations. To our knowledge, this is the first report of focused spots with the size scale of a neuron soma in brain tissue formed from implantable neural probes.

Photonic neural probe enabled microendoscopes for light-sheet light-field computational fluorescence brain imaging.

Significance: Light-sheet fluorescence microscopy is widely used for high-speed, high-contrast, volumetric imaging. Application of this technique to in vivo brain imaging in non-transparent organisms has been limited by the geometric constraints of conventional light-sheet microscopes, which require orthogonal fluorescence excitation and collection objectives. We have recently demonstrated implantable photonic neural probes that emit addressable light sheets at depth in brain tissue, miniaturizing the excitation optics. Here, we propose a microendoscope consisting of a light-sheet neural probe packaged together with miniaturized fluorescence collection optics based on an image fiber bundle for lensless, light-field, computational fluorescence imaging. Aim: Foundry-fabricated, silicon-based, light-sheet neural probes can be packaged together with commercially available image fiber bundles to form microendoscopes for light-sheet light-field fluorescence imaging at depth in brain tissue. Approach: Prototype microendoscopes were developed using light-sheet neural probes with five addressable sheets and image fiber bundles. Fluorescence imaging with the microendoscopes was tested with fluorescent beads suspended in agarose and fixed mouse brain tissue. Results: Volumetric light-sheet light-field fluorescence imaging was demonstrated using the microendoscopes. Increased imaging depth and enhanced reconstruction accuracy were observed relative to epi-illumination light-field imaging using only a fiber bundle. Conclusions: Our work offers a solution toward volumetric fluorescence imaging of brain tissue with a compact size and high contrast. The proof-of-concept demonstrations herein illustrate the operating principles and methods of the imaging approach, providing a foundation for future investigations of photonic neural probe enabled microendoscopes for deep-brain fluorescence imaging in vivo.

Implantable photonic neural probes with 3D-printed microfluidics and applications to uncaging.

Advances in chip-scale photonic-electronic integration are enabling a new generation of foundry-manufacturable implantable silicon neural probes incorporating nanophotonic waveguides and microelectrodes for optogenetic stimulation and electrophysiological recording in neuroscience research. Further extending neural probe functionalities with integrated microfluidics is a direct approach to achieve neurochemical injection and sampling capabilities. In this work, we use two-photon polymerization 3D printing to integrate microfluidic channels onto photonic neural probes, which include silicon nitride nanophotonic waveguides and grating emitters. The customizability of 3D printing enables a unique geometry of microfluidics that conforms to the shape of each neural probe, enabling integration of microfluidics with a variety of existing neural probes while avoiding the complexities of monolithic microfluidics integration. We demonstrate the photonic and fluidic functionalities of the neural probes via fluorescein injection in agarose gel and photoloysis of caged fluorescein in solution and in fixed brain tissue.

Optical Coherence Tomography Angiography in Pinguecula and Pterygium.

PURPOSE: To investigate the density of conjunctival blood vessels in normal eyes and in eyes with pinguecula or pterygium. METHODS: In this cross-sectional study, the conjunctival blood vessel density of 15 normal eyes, 15 pinguecula eyes, and 15 pterygium eyes of 43 healthy adults was assessed using optical coherence tomography angiography with an anterior segment lens adapter. The nasal surface of each eye (3 × 3 mm) was scanned 3 times to a depth of 800 µm. Conjunctival vessel density was defined as the percent of the scanned volume occupied by vessels in which blood flow was measured. RESULTS: The high reliability of data measurement was supported by good coefficients of repeatability (<10%) of the image quality score and high intraclass correlation coefficients (>0.9). The vessel density in normal conjunctivas, 52.2 ± 4.1%, was similar to that in pinguecula conjunctivas, 50.5 ± 4.7% (P = 0.3006). However, the vessel density in conjunctivas with pterygium, 63.6 ± 3.7%, was greater than that in either normal (P < 0.0001) or pinguecula (P < 0.0001) conjunctivas. CONCLUSIONS: Using optical coherence tomography angiography with an anterior segment lens adapter, the ocular surface blood vessel density was imaged and assessed with good repeatability and reliability. The blood vessel density of conjunctivas with pterygium was significantly greater than that in either normal or pinguecula conjunctivas. This suggests that, in contrast to pinguecula development, pterygium development includes angiogenesis and neovascularization.